1. Field of the Invention
One aspect of the present invention is a polymeric foam containing one or more curable resins, and more particularly, foam casting articles.
2. Background Art
There are various types of immobilization tapes and splints available on the market and described in literature. Plaster of Paris casting tapes, used since the 19th century, Fiasco and Stills, JOURNAL OF PROSTHETICS AND ORTHOTICS, 1991, 3(2), 55–58, are basically gauzes impregnated with gypsum. They are activated by immersion in water for a few seconds and then applied around joints or fractures before they set hard. The set time for Plaster of Paris tapes can be long before their maximum strength is achieved. The main disadvantages of Plaster of Paris immobilization tapes are their poor strength to weight ratios, which results in finished casts and splints that are often bulky and heavy, and poor resistance to water, which makes showering and bathing difficult.
More recently, synthetic casting and immobilization tapes and splits were developed, which consist of substrates and water curable polymeric resins. The polymeric resins can be water cured or water reactive NCO-polyurethane prepolymers, as disclosed in U.S. Pat. Nos. 4,131,114; 4,376,438; 4,433,680; 4,502,479; 4,655.208; 4,667,661; and 5,244,997. The water cured polymeric resins can be coated onto substrates which are most commonly fiberglass or polyester, as disclosed in U.S. Pat. Nos. 3,972,323; 4,502,479; 4,688,563; 4,609,578; 4,841,958; and 5,014,403. There are numerous polyisocyanate immobilization tapes available on the market. The set time of synthetic tapes is, in general, shorter than that for Plaster of Paris tapes. The synthetic casts have good resistance to water and higher strength-to-weight ratio than Plaster of Paris tapes.
Woven or knitted fiberglass fabrics are frequently utilized as substrates to carry the water curable resins, as disclosed in U.S. Pat. Nos. 4,502,479; 4,668,563; 4,609,578; and 5,014,403. The fiberglass fabric is commonly cut before application, which can results in fibers sticking out. After the water curable prepolymer resin cures and tapes harden, the fibers can protrude from the edges and can become needle-like and can penetrate the protective fabric and contact the skin resulting in cuts and skin irritation. Similar problems can occur with substrates fabricated from other woven or knitted fibers. In addition, during the cutting of cured tapes, the fiberglass particles can become air-born, which can be hazardous if inhaled. In addition, water curable polymeric resins may have insufficient adhesion to the fiberglass.
Woven or knitted polyester fibers are also widely used as substrates that carry water curable polymeric resins. Polyester tapes are softer and have better elasticity than fiberglass tapes. However, polyester substrates can be susceptible to moisture, which can affect the stability of the water curable polymeric resins and therefore shelf-stability of the tapes or splints.
Other types of immobilization tapes have been developed that utilize woven and non-woven substrates that include natural organic fabrics (e.g. cotton and wool), natural organic polymers fibers (e.g. acetate, rayon), synthetic organic polymers fibers (nylon), etc. The non-woven substrates tend to have smoother edges than woven substrates, however, they tend to be thicker, which makes it more difficult to evenly spread the water curable resins, and can lessen the moldability of tapes and splints as disclosed in U.S. Pat. Nos. 4,351,683; 4,683,877; 4,888,225; and 4,946,726.
U.S. Pat. Nos. 4,888,225 and 4,946,726 disclose orthopedic splinting articles for use with animal body parts, which comprise of a cellular material unitary blank with water curable isocyanate functional polyurethane prepolymer resin. The blank is dimensioned to extend the length of the body part to be immobilized and to partially, but not completely, extend around the circumference of the body part. These splinting articles are limited to pre-fabricated designs, manufactured from one piece and one layer of cellular material unitary blank which is one-quarter inch to one-half inch thick. It is extremely difficult to evenly load viscous curable isocyanate resins throughout such thick cellular foams blank, which can lead to suboptimal properties of cured orthopedic splinting articles.
As an alternative, U.S. Pat. Nos. 4,888,225 and 4,946,726 propose that a water-curable resin can be prepared by reacting polyol and polyisocyanate reagents in-situ in the foam substrate, which can be very difficult to control as the reagents would not necessarily get adequate mixing, which could lead to incomplete reaction and in turn to poor quality water-curable resin in the foam substrate. Furthermore, side reactions with foam substrate can occur which can further change the properties of the curable resin and the foam substrate. As a result, these splinting articles based on a one layer, unitary blank have found limited, if any, application in the orthopedic splinting applications.
U.S. Pat. No. 3,728,206 discloses a composite orthopedic supportive structure comprised of a non-woven open cell foam that is impregnated with crystalline thermoplastic material such as polyisoprene. This orthopedic supportive structure is heated to an elevated temperature until the crystalline thermoplastic material melts and it is applied to the body part while hot. The composite subsequently crystallizes and hardens when cooled down to room temperature. Additionally, the cooling of the crystalline thermoplastic material can take a relatively long time, which is undesirable in immobilization applications. Furthermore, application to the body member while hot makes the utilization of such orthopedic supportive structures extremely undesirable as it may result in burns. Therefore, these orthopedic supportive structures have found no significant, if any, application in the orthopedic immobilization applications.
In light of the foregoing, there is a need for the orthopedic immobilization tapes which are not woven and not knitted, that can be soft and flexible, can have good moldability, can have good adhesion to curable resin and that can facilitate easy loading of the resin into the substrate, and the orthopedic immobilization tapes thin enough that can be used as orthopedic winding casting tapes or layered for use in orthopedic casting splinting articles, that when cured can harden adequately to provide required immobilization.